This is Charlie Craven’s “Mole Fly”. It’s super easy to tie, but does an incredible job of imitating small mayflies and midges struggling to free themselves from their nymphal shucks in the surface film. Think blue winged olives. When it lands on the water, the entire body of the fly sinks below the surface while the CDC prevents it from dropping further and resembles an emerging wing.
A small curved shank emerger hook like a Dai-Riki #125 in size 20 works well for this pattern. Plunger-style hackle pliers make the job of mashing the barb and securing the hook in your tying vise a good bit easier.
For thread, olive 6/0 Danville is always a good choice. Start your thread behind the hook eye and take wraps to secure it to the shank. You can then break or snip the tag end off. End with your thread about an eye length behind the eye.
For the wing on this size 20, you can use either a couple of regular CDC feathers with their tips aligned, or a single CDC puff. Of course, you can use different colors of CDC but I’m not sure it matters as long as it floats. Here I’ve selected a single natural dun CDC puff. Measure to form a wing a full hook in length and then, with two wraps, bind it to the top of the hook shank. If it’s a little long, it should be fairly easy to adjust to the proper length. When you’ve got it right, take thread wraps to further secure the butts to the top of the hook shank. You can then reach in with your tying scissors and trim them off at an angle. Continue taking thread wraps to about the barb.
Beaver dubbing is used for the body of the fly because it readily takes on water and sinks. Choose or blend whatever color you think most closely resembles a partially evacuated trailing shuck. Here I’m using basic brown. Just the smallest of pinches is all you need. Pull out as many of the longer stiffer guard hairs as you can to leave only the fine underfur. Create a short thin dubbing noodle on your tying thread, you don’t want to overdub this pattern. With the noodle complete, wrap bare thread well down the hook bend and then begin to form the shuck with the dubbing noodle. If you can put a little taper into it, so much the better. When you reach the base of the wing, you should be just about out of dubbing. Pull the wing back to expose the hook eye, and take a few thread wraps behind the eye to secure it.
Get hold of your whip finish tool and, while holding the wing and thread back with your left hand, whip finish with your right. Do a 4 or 5 turn whip finish and then carefully cut or snip your tying thread free. With your fingertips, preen the CDC forward to the correct orientation. The fibers will naturally want to fan out a bit which is perfect. Do make sure the eye is free of obstruction or you’ll have problems attaching it to fine tippet.
You’ve got to love a pattern that’s so simple but does such a great job representing a mayfly in its most vulnerable state.